Base material for artificial leather

ABSTRACT

A base material for artificial leather having a water vapor absorption capacity of from 2 to 8% by weight, based on a fibre fleece impregnated with a rubber latex mixture containing a heat sensitizer, a quick-acting vulcanization accelerator and, as expanding agent, a silicone oil emulsion or an inert, emulsifiable substance which is insoluble both in the rubber and the other constituents of the latex. After the impregnation of the fibre fleece, the latex mixture is coagulated by heat, vulcanized and then dried.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 822,000 filedAug. 5, 1977 which in turn is a continuation of application Ser. No.650,532 filed Jan. 19, 1976 and now abandoned.

This invention relates to a base material for artificial leather basedon fibre fleeces impregnated with a rubber latex, and to a process forthe production of this base material. The base material for artificialleather according to the invention has a particularly high water vapourabsorption capacity which reaches about 70% to 80% of the absorptioncapacity of natural leather.

Microporous sheet-form materials permeable to water vapour and based onsubstrates impregnated with rubber latices are known from DT-AS No.1,570,088. Although these products are microporous and, hence, show acertain permeability to water vapour, they have no absorption capacityfor water vapour. The process by which they are produced is unsuitablein practice for the production of large surfaces on a commercial scalebecause the latex mixtures used are only stable for a short period and,hence, are unsuitable for continuous impregnating processes.

Accordingly, there is a need to provide a base material for artificialleather which, on the one hand, has a high water vapour absorptioncapacity and which, on the other hand, can be manufactured easily andreproducibly. The water vapour absorption capacity is particularlyimportant because it is one of the most outstanding properties ofnatural leather and, hitherto, it has never been adequately reproducedin synthetic products.

Accordingly, the present invention provides a base material forartificial leather based on a fibre fleece impregnated with a rubberlatex, which is characterised by a water vapour absorption capacity offrom 2 to 8% by weight, based on the dry weight of the material, atensile strength of from 30 to 250 kg/cm² and an elongation at break offrom 30 to 150%.

The process for producing this base material for artificial leather byimpregnating a fibre fleece with a rubber mixture, coagulating themixture, followed by vulcanisation, is distinguished by the fact that afibre fleece is impregnated with a rubber latex mixture containing aheat sensitiser, a quick-acting vulcanisation accelerator and, asexpanding agent, a silicone oil emulsion or an inert, emulsifiablesubstance which is insoluble both in the rubber and in the otherconstituents of the latex and, after coagulation of the latex mixture byheating it, is vulcanised, preferably in steam, and then dried.

Fibre fleeces suitable for the production of the artificial leather basematerial are, in particular, fleeces consisting of natural and/orsynthetic fibres. Polyamide, polyester, polypropylene, viscose andcellulose fibres are preferably used.

Rubber latices suitable for impregnation are, in principle, anyheat-sensitisable natural or synthetic rubber latices. Particularlysuitable rubber latices are natural rubber latex and synthetic rubberlatices such as, for example, carboxylated and non-carboxylated laticesbased on copolymers of butadiene/acrylonitrile, butadiene/styrene,chloroprene and butadiene/acrylic acid esters, and also isoprene andcorresponding copolymers. In addition, the polymers may contain acidamide functions and autocrosslinking groups such as, for example,N-methylol acrylamide.

Heat sensitisers which may be used in accordance with the invention are,for example, polyvinyl methyl ethers, polyethylene- and polypropyleneoxide adducts and/or their co-adducts, polyalkyl and polyaryl siloxanesand ethylene diamine polyether adducts.

Vulcanisation agents are, for example, dispersion mixtures consisting ofsulphur, zinc oxide and vulcanisation accelerators. In the case ofreactive polymers which normally crosslink in the absence of sulphur andvulcanisation accelerators, suitable crosslinking agents arecondensation products of melamine, urea or phenol with formaldehyde, ormetal oxides.

It is preferred, however, to use polymers which contain noautocrosslinking groups. For the crosslinking of these polymersaccording to the present invention the latex is compounded with amixture suitable for vulcanisation, preferably in form of a dispersionor a paste. This paste contains in addition to water, a dispersingagent, and known fillers like titanium dioxide the usual vulcanisingagents like sulfur and zinc oxide and according to the invention aquick-acting water-soluble vulcanisation accelerator besides awater-insoluble vulcanisation accelerator.

The presence of a quick-acting vulcanisation accelerator is ofparticular importance. Suitable quick-acting vulcanisation acceleratorsare, primarily, water-soluble sodium or ammonium salts of variousderivatives of dithiocarbamic acid, optionally in combination with saltsof mercaptobenzothiazole.

Quick-acting water-soluble vulcanisation accelerators are for examplethe alkaline metal, alkaline earth metal, and ammonium salts ofdimethyl, diethyl, diisopropyl and dibutyl dithiocarbamic acid.

Water-insoluble vulcanisation accelerators are for example the zincsalts of the above-mentioned dithiocarbamic acids, mercaptobenzothiazoleand its zinc salts, thiurame and its derivatives.

A suitable dispersing agent is for example the condensation product ofnaphthalene sulfonic acid and formaldehyde.

The vulcanisation paste according to the present invention is composedas follows:

0.5 to 10.0 parts by weight of zinc oxide, preferably about 5.0 parts byweight

0.2 to 10.0 parts by weight of sulfur, preferably about 2.0 parts byweight

0.2 to 3.0 parts by weight of water-soluble accelerator, preferablyabout 1.0 parts by weight

0.2 to 3.0 parts by weight of a water-insoluble accelerator, preferablyabout 1.0 parts by weight

2.0 to 15.0 parts by weight of titanium dioxide, preferably about 5.0parts by weight

0.1 to 5.0 parts by weight of a dispersing agent, preferably about 1.0parts by weight

10.0 to 50.0 parts by weight of water, preferably about 25.0 parts byweight.

The amount of vulcanisation paste to be applied may vary over a widerange. Usually 10 to 100 parts by weight, preferably 30 to 50 parts byweight, and most preferably 40 parts by weight of the vulcanisationpaste are applied on 100 parts by weight of rubber (based on the weightof dry substance).

The vulcanisation paste is prepared by adding the rest of the componentsto the water and the dispersing agent or to an according solution of thedispersing agent in water, respectively. The mixture and its ingredientsare then intensively mixed and triturated for 12 to 72 hours, preferablyfor 24 hours, for example in a roller mill. In this way a vulcanisationpaste is obtained which is ready for use and contains its ingredients ina finely divided form.

Insoluble and inert substances suitable for use as expanding agents inaccordance with the invention are:

(1) long-chain aliphatic or alicyclic isocyanates,

(2) condensates of N-methylolated melamine, urea or cyclic ureas withlong-chain fatty acids or their amides, long-chain alcohols andlong-chain amines,

(3) perfluorinated long-chain aliphatic compounds,

(4) polyvinyl methyl ethers,

(5) mixtures of epoxide resins with polyether siloxane,

(6) mixtures of polyethylene with polyether siloxane,

(7) mixtures of the products mentioned in (1) to (6).

Examples of products of this kind are stearyl isocyanate; the condensateof hexamethylolated melamine with behenic acid; perfluorinated stearicacid; polyvinyl methyl ethers having a molecular weight in the range offrom 30,000 to 70,000 and mixtures of low molecular weight polyethylenewith polyether siloxane.

Silicone oils which are particularly suitable for use as expandingagents are silicone oils having a viscosity of from 50 to 1000 cP whichare used in the form of aqueous emulsions having a solids content of,preferably, from 10 to 50% and which preferably contain non-ionicemulsifiers.

In general, the rubber latex mixture contains from 100 to 300 parts byweight, preferably about 220 parts by weight, of water; 100 parts byweight of rubber; from 0.5 to 5 parts by weight, preferably about 1.0part by weight, of heat sensitiser; from 3 to 10 parts by weight,preferably about 7.0 parts by weight, of vulcanisation agent; from 1 to4 parts by weight, preferably about 2.0 parts by weight of vulcanisationaccelerator; and from 0.5 to 10 parts by weight, preferably about 5.0parts by weight, of expanding agent.

The fibre fleece is impregnated with this mixture in the usual way, aquantity of from 50 to 200%, based on the fibres, generally being used.

The fleece thus obtained is then heated to a temperature of from 25° to80° C. Since the latex mixture contains a heat sensitiser, it is stablebelow this temperature, but coagulates very quickly above apredetermined critical temperature. After coagulation, the impregnatedfibre fleece has to be immediately vulcanised. It is important to carryout vulcanisation as quickly as possible. For this reason, vulcanisationis preferably carried out with steam at temperatures in the range from100° to 200° C. Vulcanisation generally lasts from 5 to 60 minutes. Thevulcanised, impregnated fibre fleece may then be dried in the usual way,for example in vacuo, at 100° to 170° C.

An artificial leather base material whose outstanding property is itswater vapour absorption capacity is obtained in this way. It may beprovided with a surface layer in known manner, for example by applying athin microporous polyurethane layer. It may then be finished, again inthe usual way, to give a particularly high-quality artificial leatherwhose properties substantially correspond to those of natural leather.

EXAMPLE 1

A needle-punched and subsequently shrunk random fibre fleece, consistingof 60% by weight of polyamide fibres (approximately 40 mm staple lengthand 1.5 den) and 40% by weight of polyester fibres (approximately 40 mmstaple length, 1.5 den), is impregnated with an excess of a latexmixture having the composition specified below, so that 100 g of solidsare taken up from the latex mixture per 100 g of fibre material. Theimpregnated fleece is then quickly heated to 50° C., as a result ofwhich the latex mixture gels. After vulcanisation with steam for 30minutes at 105° C., the fleece is dried in hot air. The fleece is thensplit so that the end product has the layer thickness indicated inTable 1. A microporous base material for artificial leather is obtained.The fleece has a water vapour absorption capacity of 4.4% (as determinedby the method described below).

The latex mixture used has the following composition:

210.0 parts by weight of a 47% latex of a copolymer of 85% by weight ofbutadiene and 15% by weight of acrylonitrile (=100 parts by weight ofdry substance)

10.0 parts by weight of a 50% by weight silicone oil emulsion (100-1000cP) in a 2% aqueous solution of the condensation product of 1 mol ofbenzyl phenyl phenol and 20 mols of ethylene oxide,

1.0 part by weight of a polyether siloxane,

8.0 parts by weight of benzyl phenyl phenol,

75.0 parts by weight of water,

41.0 parts by weight of a vulcanisation paste of 2 parts by weight ofcolloidal sulphur, 5 parts by weight of zinc oxide, 1 part by weight ofzinc diethyl dithiocarbamate, 5 parts by weight of titanium dioxide, 1part by weight of sodium diisopropyl dithiocarbamate and 27 parts byweight of a 5% aqueous solution of a condensation product of naphthalenesulphonic acid with formaldehyde.

The coagulation point of this latex mixture is approximately 40° C.

Comparison Test 1

This test is carried out in exactly the same way, except that neitherthe silicone oil emulsion nor the sodium diisopropyl dithiocarbamate(very quick accelerator) is added. In addition, vulcanisation is carriedout in hot air at a temperature of from 110° to 130° C. and not in asteam atmosphere. The material thus obtained has a water vapourabsorption capacity of 0.6%.

The results are summarised in Table 1. The corresponding values forskiver are also shown for comparison.

EXAMPLES 2 to 4

A random fibre fleece consisting of 60% by weight of polyamide fibres(approximately 40 mm staple length, 1.5 den) and 40% by weight ofpolyester fibres (approximately 40 mm staple length, 1.5 den), isimpregnated with an excess of a latex mixture having the compositionspecified below, so that 100 g of solids are taken up from the latexmixture per 100 g of fibre material. The impregnated fleece is thenquickly heated to 50° C., as a result of which the latex mixture gels.After vulcanisation with steam for 30 minutes at 105° C., the fleece isdried in hot air. The fleece is then split so that the end product hasthe layer thickness indicated in Table 2. A microporous base materialfor artificial leather is obtained. The fleeces have a water vapourabsorption capacity of from 4 to 5% (as determined by the methoddescribed below; cf. Table 3).

The latex mixture used has the following composition:

210.0 parts by weight of a 47% latex of a copolymer of 60.0% by weightof butadiene and 36% by weight of acrylonitrile and 4.0% by weight ofmethacrylic acid (=100 parts by weight of dry substance),

(a) 15 parts by weight of stearyl isocyanate, 33% emulsion, or

(b) 15 parts by weight of a mixture of polyether siloxane withpolyethylene, 33% emulsion, or

(c) 30 parts by weight of the condensation product of methylolatedmelamine with behenic acid, 16.5% emulsion, or

(d) 30 parts by weight of polyvinyl methyl ether, molecular weightapproximately 50,000, 16.5% emulsion,

1.0 part by weight of a polyether siloxane,

2.0 parts by weight of benzyl phenyl phenol,

75.0 parts by weight of water,

41.0 parts by weight of a vulcanisation paste of 2 parts by weight ofcolloidal sulphur, 5 parts by weight of zinc oxide, 1 part by weight ofzinc diethyl dithiocarbamate, 5 parts by weight of titanium dioxide, 1part by weight of sodium diisopropyl dithiocarbamate and 27 parts byweight of a 5% solution of a condensation product of naphthalenesulphonic acid with formaldehyde.

The coagulation point of this latex mixture is approximately 40° C.

Comparison Test 2

This test is carried out in exactly the same way, except that neitherthe inert substances which are insoluble both in the rubber and in theother constituents of the latex nor the sodium diisopropyldithiocarbamate (very quick accelerator) are added. In addition,vulcanisation is not carried out in a steam atmosphere, but in hot airat a temperature in the range of from 100° to 130° C. The material thusobtained has a water vapour absorption capacity of 0.6%.

The results are summarised in Table 2 and 3. The corresponding valuesfor skiver are also shown for comparison.

                                      Table 1                                     __________________________________________________________________________                                Tear                                                                          prop-                                                         Layer           agation                                                                            Stitch    Extension                                      thick-                                                                              Tensile                                                                            Elong-                                                                             resis-                                                                             tear re-                                                                           Repeated                                                                           (2)       Water-vapour take-                   ness  strength                                                                           ation at                                                                           tance                                                                              sistance                                                                           flexural                                                                           Pre-      up (3)                               (mm)  kp/cm.sup.2                                                                        break %                                                                            kp/cm                                                                              kp/cm                                                                              strength                                                                           ssure     after                                                                            after                                                                            after                          according                                                                           (DIN (DIN (DIN (DIN (1)  atms      4 hrs                                                                            8                                                                                24 hrs                    Direction                                                                          to IUP4                                                                             53328)                                                                             53328)                                                                             53329)                                                                             53329)                                                                             IUP 20                                                                             gauge                                                                             I% II%                                                                              %  %  %                  __________________________________________________________________________    Comparison                                                                    Test   longit-                                                                            1.0   78   90   44   69   <    3.6 25 11.5                                                                             0.6                                                                              0.6                                                                              0.6                       udinal                                                                        trans-                                                                             1.0   97   110  39   64                                                  verse                                                                  Example                                                                              longit-                                                                            0.9   58   90   27   62   <    3.2 25 10.3                                                                             4.4                                                                              4.5                                                                              4.6                       udinal                                                                        trans-                                                                             0.9   106  70   35   61                                                  verse                                                                  Skiver longit-                                                                            1.5   198  50   48   140  >    --  -- -- 5.3                                                                              5.9                                                                              6.9                       udinal                                                                        trans-                                                                             1.5   203  50   52   130                                                 verse                                                                  __________________________________________________________________________      (1)Bally-Flaxometer, flexing (dry) 200,000 times (IUP                         (2)Extension, Bally-Tensometer (IUP 13) I = linear extension                 II = permanent extension (3)By the method described below.                    <means damaged                                                                >means undamaged                                                         

    __________________________________________________________________________                Layer           Tear*                                                                              Stitch*   Extension (2)                                  thick-                                                                              Tensile*                                                                           Elong-*                                                                            prop-                                                                              tear re-  (IUP 13)                                       ness  strength                                                                           ation at                                                                           agation                                                                            sistance                                                                           Flexural*                                                                          Pre-                                           (mm)  kp/cm.sup.2                                                                        break %                                                                            resis-                                                                             kp/cm                                                                              strength                                                                           ssure                                          according                                                                           (DIN (DIN tance                                                                              (DIN (1)  atms                                      Direction                                                                          to IUP4                                                                             53328)                                                                             53328)                                                                             kp/cm.sup.2                                                                        53329)                                                                             IUP20                                                                              gauge                                                                             I% II%                         __________________________________________________________________________    Comparison                                                                    Test   longit-                                                                            1.0   78   90   44   69        3.6 25 11.5                               udinal                         <                                              trans-                                                                             1.0   97   110  39   64                                                  verse                                                                  Example                                                                              longit-                                                                            1.1   58   90   27   62        3.2 25 10.3                               udinal                         <                                              trans-                                                                             1.1   106  70   35   61                                                  verse                                                                  Skiver longit-                                                                            1.4   198  50   48   140       --  -- --                                 udinal                         >                                              trans-                                                                             1.4   203  50   52   130                                                 verse                                                                  __________________________________________________________________________      (1)Bally-Flexometer, flexing (dry) 200,000 times (IUP 20)                     (2)Extension, Bally-Tensometer (IUP 13)?                                     <means damaged                                                                >means undamaged                                                              I=linear extension                                                            II=permanent extension                                                         *These values ae substantially identical for the artificial leather          materials obtained with expanding agents a) to d).                       

                  Table 3                                                         ______________________________________                                        Water vapour uptake*                                                                    after 4  after 8    after 24                                                  hours %  hours %    hours %                                         ______________________________________                                        Comparison test                                                                           0.6        0.6        0.6                                         Skiver      5.3        6.2        6.9                                         Example a)  1.4        2.1        3.9                                         Example b)  1.7        2.2        4.4                                         Example c)  1.5        2.7        4.4                                         Example d)  1.7        2.2        4.8                                         ______________________________________                                          *by the method described below                                          

The water vapour absorption capacity was determined as follows:

The test specimens (measuring 50×20 mm) were prepared for 24 hours at20° C. in a conditioned room with a relative air humidity of 65%.Thereafter they were accurately weighed (to 0.0001 g) and thenintroduced into a conditioned room with a relative air humidity of 86%at 20° C. After storage for 4, 8 and 24 hours, they were reweighed andthe increase in weight determined to an accuracy of 0.0001 g.

The result of measurement is the percentage increase in weight based onthe weight obtained after conditioning. The results quoted are averagesof three individual results.

We claim:
 1. A vulcanization paste comprising 0.5 to 10.0 parts byweight of zinc oxide, 0.2 to 10.0 parts by weight of sulphur, 0.2 to 3.0parts by weight of a water soluble accelerator, 0.2 to 3.0 parts byweight of a water insoluble accelerator, 2.0 to 15.0 parts by weight oftitanium dioxide, 0.1 to 5.0 parts by weight of a dispersing agent and10.0 to 50.0 parts by weight of water.